The invention relates to heating, ventilating and air conditioning duct work and particularly to round duct work and particularly to fittings to connect branching ducts from main ducts. In the air conditioning, heating and ventilation industry, duct take off fittings are used at every connection between a branch duct or fitting and the main duct. Round duct work is generally preferred because it is less expensive, is readily available, is structurally sound, is easy to provide with exterior insulation and is easy to install. The primary problem in using round ductwork for mains (main ducts) is that there has been no simple and practical way to install branch duct take-off fittings.
Factories and large sheet metal shops can provide special sheet metal fittings to suit each size main duct but this requires extensive planning, special ordering and the stocking of a tremendous quantity of various sizes of fittings.
For example, it would be common to connect a 6" round branch duct to a 12", 14", 16", 18", 20", 22", 24", . . . , 36" round main duct. This would require approximately ten fittings for every branch duct take-off size. With lack on any previous practical method of connecting a round branch to a round main duct, industry has widely adopted rectangular main ducts. This allows for fairly simple connecting of branch ducts to the main. Of course using rectangular main ducts requires considerably more costs and complex fabrication methods with more labor, material, air leakage, and in recent years an environmental concern with interior duct sound and insulation lining. The lining can erode, help support mold growth and can add to interior air pollution.
There are several present methods of connecting round branch ducts to round mains. In all cases special complex sheet metal patterns are required to suit the main duct curvature for fabrication.
The fitting may include a round duct section the size of the main with a duct take off fitting formed to suit each size curvature. Another type is a special saddle that fits only one main duct size. In all cases, it takes considerable labor, time, complex calculations and special equipment to fabricate these fittings. Due to these complexities many sheet metal installers, change the main duct to rectangular ductwork because of the ease of installing fittings. Rectangular ductwork is less efficient, less rigid, has a greater pressure drop for a given cross-sectional area, and is more costly to fabricate, install, and insulate than round ductwork.
The prior art include U.S. Pat. Nos.
3,915,477 PA1 3,998,480 PA1 4,009,894 PA1 4,249,758 PA1 4,418,943 PA1 4,491,124 PA1 4,569,110 PA1 4,573,715 PA1 4,620,729
The apparatus described therein does not allow for interconnection of a range of round duct sizes.
An object of this invention is to provide a simple means of connecting round branch ducts to any size round main duct.
It is an object of the invention to provide a simple and practical way to install branch duct take-off fittings.
It is another object of the invention to provide apparatus which will fit a wider range of main duct sizes and thus inventories for such apparatus may thus be maintained at less than one tenth the quantity required for prior art fittings.
Still another object of the invention is to provide apparatus which permits easy installation of exterior insulation of the main round duct in a manner that is simple and inexpensive.
It is an object of the invention to provide apparatus which is inexpensive to manufacture and which requires a minimum of labor to install.